Sprinklers for discharging fire-extinguishing fluid in response to heat activation of a heat responsive member associated with each sprinkler have been known for many years. There are many designs for such sprinklers. Many of these designs have an orifice for discharging the fire-extinguishing fluid at one end of a box-like frame and a deflector at an opposite end of the frame for dispersing the fluid discharged from the orifice. A cap is placed over the orifice and a structure extends from the cap across the opening defined by the frame to the deflector end of the frame for normally holding the cap on the orifice to prevent discharge of the fluid. The cap-retaining structure has a heat fusible portion which responds to heat as from a fire to permit the structure to move from its cap-retaining position to release the fluid.
Even though the function and structural requirements of such sprinklers are well-known, the many designs for such sprinklers indicate the difficulty of providing a structure which best meets all the requirements of the sprinkler. The sprinklers must disperse the fluid over a predetermined and substantial area to permit predetermination of a pattern of the minimum number of sprinklers required for discharging fire-extinguishing fluid over the entire area to be protected by a sprinkler system. As safety equipment for the extraordinary conditions of an unexpected fire, the sprinklers must remain closed to prevent unwanted and damaging discharge of fluid for the substantial time during which no fire exists, but be highly reliable for discharging the fire-extinguishing fluid if and when, at some remote time after installation, a fire does occur in the area protected by the sprinkler system. In addition, it is esthetically desirable that the sprinklers be both inconspicuous and, when observed, as attractive as possible.
Long experience with sprinklers and careful observation of their operation has determined that a sprinkler structure having a deflector across an open frame from a fluid discharge orifice is a highly desirable way of properly dispersing fire-extinguishing fluid over a substantial area. However, such operation requires that the position of the structure normally retaining the cap over the fluid discharge orifice after it releases the cap be known for determining its affect on the pattern of the fluid dispersed by the sprinkler. In many sprinkler designs, it is intended to have the retaining structure fall from the sprinkler when it releases the cap so as to avoid interference with the pattern of the discharged fluid. In such designs, it would be a malfunction of the sprinkler to have the cap-retaining structure block a portion of the fluid even if the structure operates sufficiently to permit fluid discharge. The area in which the structure blocked the fluid discharge would then not receive fire-extinguishing fluid and the sprinkler system would fail to protect the entire area for which it was designed.
Reliable operation of sprinklers at an unpredictable and often remote time after installation is also difficult to achieve. The cap retaining structure must be strong enough to prevent discharge of fluid when no fire is present which would unnecessarily damage property in the area protected by the sprinkler system. The cap-retaining strength of the structure also must be sufficient to resist vibration, accidental bumping, cleaning, and other contact which is not intended to initiate the discharge of fluid. In spite of the strength required of the cap-retaining structure, the structure still must timely release the cap when a fire activates the heat responsive member in the structure. Dust and dirt accumulated over the years since the sprinkler was installed must not interfere with its operation. In addition, paint which often is accidentally sprayed onto the sprinkler during painting of the structure such as a ceiling adjacent the sprinkler should have a minimum tendency to prevent operation of the sprinkler.
Modern tastes in design tend to prefer simpler, functionally oriented appearances. Such structures should not have unnecessary projections or gewgaws and additionally should be sufficiently small to make the sprinklers as inconspicuous as possible. Such design functionally contributes to the reliability of operation of the sprinkler by providing a minimum of projections which could hang up on other parts and a minimum of joints and interacting parts which accumulated dust, dirt, or paint could cause to malfunction.
One sprinkler design which attempts to meet all these well-understood but difficult-to-achieve objectives has a box frame extending from a capped fluid discharge orifice to an oppositely disposed fluid deflector. An O-shaped strut extends from the cap to an end portion of a generally S-shaped lever pivoted against a compression screw at the deflector end of the frame. The S-shaped lever extends from the end portion at the screw around one side of the strut, through its central opening, and then parallel to the strut to engage a side of a cylindrical retaining assembly. The retaining assembly has a dome-like projection at one end and a ball extending from the other end which engage opposite sides of the central opening in the O-shaped strut to hold the lever and strut in cap-retaining position. The ball is normally held in the end of the retaining assembly by a disk which is held in place by an eutectic material in the cylinder of the retaining assembly. Heat from a fire then melts the eutectic to permit the disk and ball to slide into the cylinder. In proper operation, the cylinder then pivots about the projection on its other end to pass through the central opening in the O-shaped strut and release the lever and strut from their cap-retaining position, all of the cap-retaining structure then falling from the sprinkler. However, the dome-like projection on the cylinder urges the cylinder laterally across the opening in the strut so that the ball-end of the cylinder may catch on the strut or dust, dirt or paint accumulated about the opening in the strut. If the cylinder is so prevented from passing through the opening, proper operation of the sprinkler may be prevented. In addition, the O-shaped strut configuration requires the cap-retaining structure to have a wider elevation and thus be more conspicuous than a strut without a central opening.